Technical Abstract:
Since 1923 when Sax demonstrated that a quantitative trait locus (QTL) could be associated with a marker locus in bean, geneticists have been trying to identify the genes responsible for variation in complex or quantitative traits. Although QTL of agricultural interest focus primarily on production and disease resistance phenotypes, such QTL are only a subset tof the group of complex, multigenic traits that also include behavior and development that are under study in humans and a variety of other species. Thus, QTL are of fundamental importance not only in agriculture, but throughout all of genetics. In theory, identification of a QTL is very simple. First, genetic markers spaced throughout the genome are genotyped on a group of related individuals segregating for the trait(s) of interest. Second, statistical analysis determines if the inheritance pattern of alleles at a marker locus correlates with expression of the trait, thereby indicating genetic linkage of the marker to a QTL. Over the 74 years sinc the Sax report, QTL research has relied mainly on the use of theoretical models of their effects and distribution. With the advent of DNA-based techniques, the number of useful genetic markers is no longer limiting, and it is now possible to perform a systematic genome-wide screen to detect marker-QTL linkages. Thus, the key to tapping into the information stored in the genome has been the development of comprehensive genetic maps based on DNA marker technology.